Coenzyme Q is an essential component widely distributed in living organisms from bacteria to mammals. It is known that human coenzyme Q is mainly composed of coenzyme Q10, having 10 repeat structures in its side chain. Coenzyme Q10 is a physiological component present as a constituent component of the mitochondrial electron transport system in the cell of the living body. It functions as a transport component in the electron transport system by repeating oxidation and reduction in the living body.
Coenzyme Q10 is known to show energy production, membrane stabilization and antioxidant activity in the living body, and has a high degree of usability. Coenzyme Q10 occurs in two forms, the oxidized form and the reduced form, and it is known that, in the living body, usually about 40 to 90% of the coenzyme exists in the reduced form. Of coenzymes Q10, oxidized coenzyme Q10 (aka. ubiquinone or ubidecarenone) is widely used for pharmaceutical field as a drug for congestive heart failure. Besides the pharmaceutical use, it is widely used as an agent for oral preparation and a skin preparation, or as a nutritional product or a dietary supplement, like vitamin.
On the other hand, reduced coenzyme Q10 shows higher oral absorbability than oxidized coenzyme Q10, and is a superior compound effective as food, Food with nutrient function claims, Food for specified health uses, nutritional supplement, nutritional product, animal drug, drink, feed, pet food, cosmetic, pharmaceutical product, therapeutic drug, prophylactic drug and the like.
However, reduced coenzyme Q10 is easily oxidized by molecular oxygen into oxidized coenzyme Q10, and therefore, stabilization of reduced coenzyme Q10 is an important issue when it is processed into a food, food with nutrient function claims, food for specified health use, nutritional supplement, nutritional product, animal drug, drink, feed, pet food, cosmetic, pharmaceutical product, therapeutic drug, prophylactic drug and the like, or a material or composition therefor, or during handling after processing and the like. Complete removal or blocking of oxygen during the above-mentioned handling is extremely difficult and remaining or admixed oxygen particularly during heating for processing and long-term preservation exerts a markedly adverse effect. The above-mentioned oxidation is directly related to quality problems such as the by-product oxidized coenzyme Q10.
As mentioned above, stable retention (protection from oxidation) of reduced coenzyme Q10 is an extremely important problem, for which little study has been done as to the method and composition for stably retaining reduced coenzyme Q10. There are only a report on a composition concurrently containing a reducing agent and a production method thereof (WO01/052822) and a report on stabilization of reduced coenzyme Q10 in fat and oil (WO03/062182).
WO01/052822 discloses methods for preparing    1) a composition comprising reduced coenzyme Q10 and an amount of a reducing agent effective to prevent the oxidation of reduced coenzyme Q10 to oxidized coenzyme Q10; and an amount of a surfactant or a vegetable oil or a mixture thereof, and optionally, a solvent effective to solubilize the above-mentioned reduced coenzyme Q10 and the aforementioned reducing agent,    2) a composition for oral administration obtained by formulating the above-mentioned composition into a gelatin capsule or tablet,    3) the above-mentioned composition containing reduced coenzyme Q10 by the use of oxidized coenzyme Q10 and a reducing agent in situ.
However, the above-mentioned WO01/052822 does not contain a detailed description relating to the quality, stabilizing effect and the like of reduced coenzyme Q10 contained in the composition. In addition, the above-mentioned composition and preparation method thereof are highly complicated and troublesome because the composition plays multiple roles (i.e., role of reaction field for reducing oxidized coenzyme Q10 to reduced coenzyme Q10 and role of stably retaining reduced coenzyme Q10). It is generally known that ascorbic acids (reducing agents) encapsulated in a gelatin capsule degrade disintegrability of the gelatin capsule, which in turn exerts an adverse influence on the absorbability in the living body.
Furthermore, it should be noted that since the above-mentioned composition and preparation method thereof use a reaction mixture as it is, the safety is not entirely secured. To be specific, ascorbic acids used as reducing agents for reducing oxidized coenzyme Q10 to reduced coenzyme Q10 are oxidized to give a considerable amount of dehydroascorbic acids, which remain in the above-mentioned compositions. The dehydroascorbic acids and oxalic acid produced by decomposition are highly harmful unlike ascorbic acids. For example, an increase in the lipoperoxide amount and a decrease in the antioxidant substance in the liver and kidney, as well as an increase in the amount of oxalic acid in the kidney have been reported, and side effects such as lower resistance to oxidative stress, easy onset of ureteral calculus and the like are feared.
In addition, WO03/062182 discloses, as a method for protecting reduced coenzyme Q10 from oxidation, a stabilizing method of reduced coenzyme Q10, comprising forming a composition containing reduced coenzyme Q10, fats and oils (excluding olive oil) and/or polyol as a main component, which does not substantially inhibit stabilization of reduced coenzyme Q10. However, the aforementioned stabilizing method may be insufficient to ensure stability of reduced coenzyme Q10.
Moreover, the compositions described in WO01/052822 and WO03/062182 are oily compositions wherein reduced coenzyme Q10 is dissolved in fats and oils and/or surfactant. Thus, the applicable ranges thereof are limited. Under the circumstances, there is a demand for a composition containing powdery and stable reduced coenzyme Q10, which can be used for various applications.